In the LTE (Long Term Evolution) radio technology specified by 3GPP (3rd Generation Partnership Project) a UE (user equipment) may utilize dual connectivity for achieving enhanced performance of data transmission between the UE and a cellular network. In the case of dual connectivity, the UE may simultaneously utilize two radio links for sending and/or receiving data. Such dual connectivity features are for example discussed in 3GPP TR 36.842 V12.0.0 (December 2013).
Further, it is also known to combine a cellular radio link, such as an LTE radio link, with a WiFi radio link. For example, 3GPP TS 23.261 V12.0.0 (September 2014) describes a seamless Wireless Local Area Network (WLAN) offloading mechanism, which may be used by a UE to simultaneously connect to a 3GPP access and a WLAN access and transmit some IP (Internet Protocol) flows (e.g., best effort traffic) over the WiFi radio link and the WLAN access to the Internet while other IP flows (e.g., traffic with specific QoS requirements) are transmitted via the cellular radio link. In this case, the distribution of the traffic over the different radio links is organized on the IP layer. For example, this means that a first IP flow from the UE to a certain IP destination address would be routed via the WiFi radio link, while a second IP flow from the UE to another IP destination address would be routed via the cellular radio link.
The cellular radio link may be regarded as a scheduled link. That is to say, radio resources used by the cellular radio link are controlled by the cellular network. For example, as specified in 3GPP TS 36.321 V12.3.0 (September 2014) for the LTE radio technology, the UE may need to request allocation of radio resources by the eNB before it can transmit data on the LTE radio link. The allocation of resources may be requested explicitly by sending a scheduling request (SR) or implicitly by sending a buffer status report (BSR). The BSR may be included in an uplink transmission of data and indicates an amount of uplink data which still needs to be transmitted by the UE. The eNB indicates the allocated radio resources by sending an uplink grant to the UE, and the UE transmits the data by performing a radio transmission on the allocated radio resources.
As compared to that, the WiFi radio link may be regarded as an unscheduled link where the UE can transmit data without requesting allocation of resources. In the case of the WiFi link, a contention based mechanism is applied for handling colliding radio transmissions on radio resources shared by multiple devices.
In view of better utilizing different available access technologies, it may be desirable to more closely aggregate a cellular radio link and a WiFi radio link, e.g., in such a way that also traffic of the same IP flow may be distributed over different radio links. However, since the cellular radio link is a scheduled link while the WiFi radio link is an unscheduled link, this is not straightforward. For example, the cellular radio link and the WiFi radio link may have different characteristics concerning latency or throughput performance, and such characteristics may also depend on various conditions.
Accordingly, there is a need for techniques which allow for efficiently combining scheduled transmissions and unscheduled transmissions.